Chinese claims to an ancient kingdom regarded by Koreans as part of the origins of modern-day Korea continue to provoke angry protests on the peninsula, with accusations that Seoul is failing to pursue the issue for fear of upsetting Beijing.

At the centre of the historical dispute is the kingdom of Balhae (698-926AD), which straddled parts of modern-day Manchuria, Russia's Primorsky Krai, and the northern part of the Korean peninsula.

Korean historians say Balhae was founded by descendants of the ancient Korean kingdom of Koguryo, including Korean general Tae Cho-young. But recently released papers from the Beijing-funded Research Centre for Chinese Borderland History and Geography claim Bohai, as it is known in Chinese, was created by minority tribes in China and that it was a vassal state with a history closely tied to China.

The dispute has ignited angry demonstrations in Seoul, with protesters calling on Koreans to boycott China as a travel destination. The claims have also been condemned by South Korean politicians across the political divide.

'The distortion of history is another form of invasion,' said Kim Geun-tae, chairman of the ruling Uri Party.

In recent years, South Korean scholars have grown increasingly alarmed at what they view as an attempt to hijack Korea's past.

'If they are not stopped, a huge part of Korean history will be literally stolen away from Korea' said Song Ki-ho, a leading expert on the history of Balhae kingdom.

The dispute has crucial geopolitical implications. South Korean academics believe Beijing is using history to tighten its grip on Korean-Chinese minorities, while trying to forestall any future claims by a unified Korea over the mainland's northeastern provinces.

'The Chinese are making preparations against the possibility that following reunification between North and South Koreans, Koreans might try to reclaim land which currently makes up Chinese territory,' Professor Song said.

Local media has suggested Beijing is also laying the groundwork in case of a collapse of North Korea. In a bid to guarantee its territorial integrity, Beijing could enter the North using its historical claim as justification, they say.

The South Korean government has said it will issue a full response after examination of the Chinese papers, while fending off criticism that it has adopted a lukewarm response for political reasons.

'South Korea is weak compared to its neighbour, and China holds a lot of sway because of its role in the six-party talks [over North Korea's nuclear weapons] and economic relations,' said Im Hyo-jai, of Seoul National University.

China is South Korea's largest trading partner and is also considered to wield the greatest influence over North Korea.

But Seoul has rejected accusations that it is soft-pedalling. 'The government has taken clear and resolute measures against acts distorting our history or territorial rights without linking those issues to others. China is no exception,' said Lee Kyu-hyung, the vice-minister of foreign affairs.

This dispute is an extension of a historical argument two years ago over competing claims to the kingdom of Koguryo. In 2004, as the issue threatened to sour bilateral ties, China and South Korea undertook not to escalate the argument.